There are three forms of meniscus coating processes which are commonly grouped under the term "free meniscus coating": Withdrawal processes, drainage processes, and continuous processes. Many other coating processes use a meniscus to produce films on the substrate to be coated. These include roll coating, blade coating, and slot coating.
Withdrawal coating (often referred to as dip coating) is the most common free meniscus technique used in both laboratories and industry because of its simplicity and cost. Continuous coating is often desirable because of higher output, but the complicated engineering involved often prevents it from being utilized. Drainage is based upon the same principles as withdrawal and is advantageous when space is limited since it requires no mechanical lifting mechanism. See, e.g., C. Brinker et al., in Liquid Film Coating, 673-708 (S. Kistler and P. Schweizer eds. 1997).
Free meniscus coating is a solvent intensive process and accounts for a considerable use of environmentally undesireable solvents. Accordingly, there is a need for new free meniscus coating methods and apparatus that reduce or eliminate the use of solvents such as VOCs and the use of solvents such as CFC, HCFC, HFC, or PFC solvents, as well as aqueous solvents.